Control unit and control method for reductant supply system

ABSTRACT

There are provided a control unit and a control method for a reductant supply system, which are capable of reducing energy consumption by immediately stopping heating means in the case of entering an idling stop mode. A control unit which performs control of a reductant supply system includes an idling stop determination portion that determines whether an internal combustion engine is stopped by idling stop control that automatically stops the internal combustion engine, a heating means operation determination portion that determines whether the heating means provided in the reductant supply route that supplies the liquid reductant to the reductant injection valve is in operation, and a heating means control portion that stops operation of the heating means in a state where the internal combustion engine is automatically stopped and the heating means is in operation.

TECHNICAL FIELD

The present invention relates to a control unit and a control method for a reductant supply system that is used in an exhaust gas purification device. Particularly, the present invention relates to a control unit and a control method for a reductant supply system that is used in a vehicle equipped with an idling stop system.

BACKGROUND ART

Generally, exhaust gas discharged from an internal combustion engine, such as a diesel engine, contains nitrogen oxides (hereinafter referred to as NO_(X)) that may have an impact on the environment. As an exhaust gas purification device used to purify NO_(X), an exhaust gas purification device (an SCR system) is known which injects and supplies a liquid reductant, such as a urea aqueous solution, into exhaust gas on the upstream side of a reduction catalyst disposed in an exhaust gas passage, and which selectively reduces and purifies NO using the reduction catalyst.

Note that the liquid reductant may freeze at a cold temperature, and thus the reductant may not be injected and supplied. For this reason, an exhaust gas purification device is known in which heating means is provided in a storage tank or a supply system of a liquid reductant in order to inhibit freezing of the liquid reductant.

More specifically, an exhaust gas purification device is disclosed in which heating wires are arranged over the whole or main part of the storage tank and the supply pipe system of the liquid reductant, and a heat insulating material layer is provided on the heating wires. Further, if necessary, heating wire heating means is also provided inside the storage tank, and electricity is externally supplied to the heating wires and the electricity is shut off in accordance with the outside air temperature and/or the temperature of the reductant. Thus, it is possible to maintain an appropriate temperature range in which freezing of the liquid reductant is inhibited (see Patent Document 1).

On the other hand, in recent years, in order to reduce exhaust gas discharged from internal combustion engines with the aim of environment protection and noise prevention, an idling stop system is being used that automatically stops an internal combustion engine when the internal combustion engine is temporarily stopped. The idling stop system stops the internal combustion engine while a key switch is on, and there is a possibility that the liquid reductant will be injected regardless of the fact that there is no exhaust gas flow. To address this, an idling stop system that works in coordination with the reductant supply system has been proposed.

More specifically, an idling stop system is disclosed in which the engine is stopped in an operation region where there is no problem even if the engine is automatically stopped, i.e., when the vehicle is temporarily stopped and the injection supply of the liquid reductant is continuously stopped for a predetermined period of time. Thus, it is ensured that the solute of the liquid reductant is not precipitated in an exhaust system of the engine (see Patent Document 2).

Patent Document 1: Japanese Patent Application Publication No. JP-A-2000-27627 (full text, FIG. 1)

Patent Document 2: Japanese Patent Application Publication No. JP-A-2006-118413 (full text, FIG. 1)

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

With the idling stop system described in Patent Document 2, the liquid reductant is not supplied to the exhaust system of the engine after the engine is automatically stopped. However, the process of the reductant supply system after that is not particularly taken into consideration.

Further, in an idling stop state, while the engine is stopped, the key switch remains in an on state. Therefore, in the case of the exhaust purification device that includes the heating wire heating means described in Patent Document 1, the heating wire heating means may be actuated when it is determined that the outside air temperature and/or the temperature of the reductant has decreased, regardless of the fact that the engine is stopped and injection' control of the reductant is not being performed. As a result, energy that actuates the heating wire heating means is pointlessly consumed.

To address this, the inventors of the present invention have made strenuous efforts, and have found that the above-described problems can be solved by stopping the operation of heating means when an internal combustion engine is automatically stopped by idling stop control, in a reductant supply system used in an exhaust gas purification device for an internal combustion engine equipped with an idling stop system. Thus, the present invention has been achieved. More specifically, it is an object of the present invention to provide a control unit and a control method for a reductant supply system that is capable of reducing energy consumption by stopping heating means when the internal combustion engine is automatically stopped by idling stop control.

Means for Solving the Problems

In order to solve the problems described above, according to the present invention, there is provided a control unit that performs control of a reductant supply system which is used in an exhaust gas purification device that injects and supplies a liquid reductant to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst, the reductant supply system having a storage tank that stores the liquid reductant, a pump that pressure-feeds the liquid reductant stored in the storage tank, a reductant injection valve that controls a supply amount of the liquid reductant that is pressure-fed by the pump, and a reductant supply passage through which the liquid reductant is caused to flow. The control unit for the reductant supply system is characterized by including: an idling stop determination portion that determines whether the internal combustion engine is stopped by idling stop control that automatically stops the internal combustion engine; a heating means operation determination portion that determines whether heating means provided in a reductant supply route that supplies the liquid reductant to the reductant injection valve is in operation; and a heating means control portion that stops operation of the heating means in a state where the internal combustion engine is automatically stopped and the heating means is in operation.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the heating means control portion stops the operation of the heating means when a predetermined period of time elapses after it is determined that the internal combustion engine has been automatically stopped.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the control unit further includes an outside air temperature detection portion that detects outside air temperature information. It is desirable that the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the control unit further includes an energy detection portion that detects a magnitude of energy supplied from a source of power of the heating means. It is desirable that the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the magnitude of the energy.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the control unit further includes a reductant return control portion that causes the liquid reductant of the reductant supply system to be collected into the storage tank when the internal combustion engine is automatically stopped.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the reductant return control portion collects the liquid reductant when a predetermined period of time elapses after it is determined that the internal combustion engine has been automatically stopped.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the idling stop determination portion determines that the internal combustion engine has been automatically stopped when at least a key switch of the internal combustion engine is on and when a rotational speed of the internal combustion engine continues to be equal to or less than a predetermined value for a predetermined period of time.

Further, with the structure of the control unit for the reductant supply system according to the present invention, it is desirable that the idling stop determination portion determines whether the internal combustion engine has been automatically stopped, based on a signal from an engine control unit that performs operation control of the internal combustion engine.

Furthermore, according to another aspect of the present invention, there is provided a control method for a reductant supply system which is used in an exhaust gas purification device that injects and supplies a liquid reductant to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst, the reductant supply system having a storage tank that stores the liquid reductant, a pump that pressure-feeds the liquid reductant stored in the storage tank, a reductant injection valve that controls a supply amount of the liquid reductant that is pressure-fed by the pump, and a reductant supply passage through which the liquid reductant flows. The control method for the reductant supply system is characterized by including the steps of: determining whether heating means provided in a reductant supply route is in operation in a state where the internal combustion engine is stopped by idling stop control that automatically stops the internal combustion engine; and stopping operation of the heating means when the heating means is in operation.

ADVANTAGE OF THE INVENTION

The control unit for the reductant supply system according to the present invention includes the heating means control portion that stops operation of the heating means when the internal combustion engine has been automatically stopped by the idling stop control. Therefore, the operation of the heating means is stopped, in a state where injection control of the reductant is not performed regardless of the fact that the key switch is on. Thus, wasteful consumption of energy can be suppressed.

Further, in the control unit for the reductant supply system according to the present invention, the operation of the heating means is stopped when a predetermined period of time elapses after the internal combustion engine has been automatically stopped by the idling stop control. Therefore, if an idling stop mode is cancelled in a short time and the internal combustion engine is restarted, it is possible to avoid the temperature of the reductant supply route decreasing while the internal combustion engine is automatically stopped. Thus, freezing of the liquid reductant is inhibited.

Further, in the control unit for the reductant supply system according to the present invention, the time period from when the internal combustion engine is automatically stopped by the idling stop control until when the operation of the heating means is stopped is changed in accordance with the outside air temperature. As a result, in a situation in which the liquid reductant is more likely to freeze, the heating means operates for a relatively long period of time. On the other hand, in a situation in which the liquid reductant is relatively unlikely to freeze, the operation of the heating means is stopped immediately. Thus, wasteful consumption of energy can be suppressed.

Further, in the control unit for the reductant supply system according to the present invention, the time period from when the internal combustion engine is automatically stopped by the idling stop control until when the operation of the heating means is stopped is changed in accordance with the state of the energy supplied from the source of power of the heating means. As a result, when the remaining amount of the energy is reduced, the heating means is stopped at an early timing. On the other hand, when the remaining amount of energy is sufficient, the timing at which the heating means is stopped is determined while taking into account the collection state of the liquid reductant.

Further, in the control unit for the reductant supply system according to the present invention, after the internal combustion engine is automatically stopped by the idling stop control, the liquid reductant in the reductant supply route is collected into the storage tank. As a result, it is possible to inhibit freezing of the liquid reductant in the reductant supply route, in a state where the injection control of the reductant is not performed regardless of the fact that the key switch is on.

Further, in the control unit for the reductant supply system according to the present invention, the liquid reductant is collected when the predetermined period of time elapses after the internal combustion engine has been automatically stopped by the idling stop control. As a result, if the idling stop mode is cancelled in a short time and the internal combustion engine is restarted, injection supply of the liquid reductant is restarted without delay.

Further, in the control unit for the reductant supply system according to the present invention, when a predetermined condition is established, it is determined that the internal combustion engine has been automatically stopped by the idling stop control. Therefore, control of the heating means control portion is performed in correlation with the timing at which the internal combustion engine is automatically stopped by an idling stop system.

Further, in the control unit for the reductant supply system according to the present invention, it is determined that the internal combustion engine has been automatically stopped by the idling stop control based on the signal from the engine control unit. As a result, the structure of the control unit is simplified. In addition, control of the heating means control portion is performed reliably in correlation with the timing at which the internal combustion engine is automatically stopped by the idling stop system.

Further, in the control method for the reductant supply system according to the present invention, the operation of the heating means is stopped when the internal combustion engine is automatically stopped by the idling stop control. As a result, it is possible to inhibit wasteful consumption of energy caused by the heating means operating in a state where the injection control of the reductant is not performed regardless of the fact that the key switch is on.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of the structure of an exhaust gas purification device.

FIG. 2 is a block diagram showing an example of the structure of portions relating to idling stop control of an engine control unit (ECU) provided in the exhaust gas purification device.

FIG. 3 is a block diagram showing an example of the structure of a control unit (DCU) of a reductant supply system provided in the exhaust gas purification device.

FIG. 4 is a flowchart showing an example of a method for stopping operation of heating means.

FIG. 5 is a flowchart showing an example of a method for collecting a liquid reductant into a storage tank.

FIG. 6 is a flowchart showing an example of the idling stop control.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment relating to a control unit and a control method for a reductant supply system of the present invention will be described concretely with reference to the appended drawings. However, the embodiment is just one form of the present invention and in no way limits the present invention, and any modification can be made within the scope of the present invention.

Note that, in the respective drawings, structural members that are the same are denoted with the same reference numerals, and explanation thereof is omitted as appropriate.

1. Exhaust Gas Purification Device

First, an example of the structure of an exhaust gas purification device, in which a control unit for a reductant supply system of the present embodiment is provided, will be described with reference to FIG. 1.

An exhaust gas purification device 10 shown in FIG. 1 injects and supplies a urea aqueous solution serving as a liquid reductant to the upstream side of a reduction catalyst 13 disposed in an exhaust gas passage. The exhaust gas purification device 10 selectively reduces and purifies NO_(x) contained in exhaust gas using the reduction catalyst 13. The exhaust gas purification device 10 includes, as main elements, the reduction catalyst 13 and a reductant supply system 20. The reduction catalyst 13 is arranged in the middle of an exhaust pipe 11 that is connected to an internal combustion engine 5, and selectively reduces NO_(x) contained in exhaust gas. The reductant supply system 20 includes a reductant injection valve 31 that injects and supplies the reductant into the exhaust pipe 11, on the upstream side of the reduction catalyst 13.

2. Reductant Supply System

The reductant supply system 20 provided in the exhaust gas purification device 10 of the present embodiment includes: the reductant injection valve 31 that is fixed to the exhaust pipe 11 on the upstream side of the reduction catalyst 13; a storage tank 50 that stores the liquid reductant; a pump module 40 having a pump 41 that pressure-feeds the reductant from the storage tank 50 to the reductant injection valve 31; and a control unit (hereinafter referred to as a “DCU: dosing control unit”) 60 that performs control of the reductant injection valve 31 and the pump 41 in order to control an injection amount of the reductant that is injected and supplied into the exhaust pipe 11. Further, the pump module 40 and the reductant injection valve 31 are connected by a first supply passage 58. The storage tank 50 and the pump module 40 are connected by a second supply passage 57. Furthermore, the pump module 40 and the storage tank 50 are connected by a circulation passage 59.

Further, in the example of the exhaust gas purification device 10 shown in FIG. 1, a control unit (hereinafter referred to as an “ECU: engine control unit”) 70 for controlling an operation state of the internal combustion engine 5 is connected to the DCU 60. Information about the operation state of the internal combustion engine, such as a fuel injection amount, an injection timing and a rotational speed of the internal combustion engine 5, is output.

Note that, in the present embodiment, the ECU 70 and the DCU 60 are structured as separate control units. However, the ECU 70 and the DCU 60 may be structured as a single control unit. In addition, respective signals input into and output from the DCU 60 may be transmitted via CAN.

The storage tank 50 is provided with a temperature sensor 51 for detecting the temperature of the liquid reductant stored inside the storage tank 50, and a heater 91 for heating the liquid reductant. The value detected by the temperature sensor 51 is output to the DCU 60 as a signal. When the temperature of the liquid reductant is equal to or less than a predetermined value, the heater 91 is energized. For example, a heating wire is used as the heater 91. However, this is just one example, and a known device can be used as appropriate.

Further, the pump module 40 is provided with the pump 41. The pump 41 pumps the liquid reductant in the storage tank 50 via the second supply passage 57, and pressure-feeds the liquid reductant to the reductant injection valve 31 via the first supply passage 58. The pump 41 is, for example, an electric gear pump, and is duty-controlled by a signal transmitted from the DCU 60. Further, a pressure sensor 43 is provided in the first supply passage 58, and the value detected by the pressure sensor 43 is output to the DCU 60 as a signal. The drive duty of the pump 41 is controlled such that the pressure value in the first supply passage 58 is maintained at a predetermined value. More specifically, in a state where the pressure in the first supply passage 58 becomes lower than the predetermined value, the drive duty of the pump 41 is controlled to be increased. Conversely, in a state where the pressure in the first supply passage 58 becomes higher than the predetermined value, the drive duty of the pump 41 is controlled to be reduced.

Note that, the term “drive duty of the pump” means the ratio of a pump drive time taken in one cycle, in a pulse width modulation (PWM) control.

In addition, a main filter 47 is provided in the first supply passage 58, and foreign matter contained in the liquid reductant that is pressure-fed to the reductant injection valve 31 is caught. Further, the circulation passage 59 is provided such that it diverges from the first supply passage 58 between the pump 41 and the main filter 47, and the circulation passage 59 is connected to the storage tank 50. An orifice 45 is provided in the middle of the circulation passage 59, and a pressure control valve 49 is provided closer to the storage tank 50 than the orifice 45. With the provision of the circulation passage 59 structured as described above, when the pressure value in the first supply passage 58 exceeds the predetermined value in a state where the liquid reductant is pressure-fed by the pump 41 that is feedback controlled based on the detection value of the pressure sensor 43, the pressure control valve 49 is opened and a part of the liquid reductant flows back into the storage tank 50. For example, a known check valve or the like can be used as the pressure control valve 49.

Further, a reverting valve 71 is provided in the pump module 40. When the reductant supply system 20 does not perform injection control of the liquid reductant, the liquid reductant in a reductant supply route, which includes the pump module 40, the reductant injection valve 31, the first supply passage 58 and the second supply passage 57, is collected into the storage tank 50. Therefore, when the internal combustion engine 5 is stopped and the control of the reductant supply system 20 is not performed in a cold condition, i.e., under a temperature condition in which the liquid reductant is likely to freeze, freezing of the liquid reductant in the reductant supply route is prevented. When the operation of the internal combustion engine is restarted after that, injection control of the liquid reductant is performed without delay.

For example, an on-off valve that is on-off controlled by a control signal from the DCU 60 is used as the reverting valve 71. When the reverting valve 71 is opened, the liquid reductant is collected in the storage tank 50.

Further, for example, an on-off valve that is on-off controlled by duty control is used as the reductant injection valve 31. The liquid reductant that is pressure-fed from the pump module 40 to the reductant injection valve 31 is maintained at a predetermined pressure. When the reductant injection valve 31 is opened by a control signal transmitted from the DCU 60, the reductant is injected into the exhaust gas passage.

Moreover, heaters 92 to 97 are provided in respective sections of the reductant supply route in the reductant supply system 20. The heaters 92 to 97 are provided in order to prevent a case where, if the liquid reductant is present in the reductant supply route in a cold condition, the liquid reductant freezes and clogs the reductant supply route partially or completely, thus inhibiting the reductant injection control from being performed accurately by the reductant injection valve 31. Further, energization of the heaters 92 to 97 is controlled by the DCU 60. When it is determined that the reductant supply route is under a temperature condition in which freezing of the liquid reductant may occur, based on, for example, the temperature of the liquid reductant, the outside air temperature or the like, voltage is supplied from a battery and heating is performed.

The heaters 92 to 97 are not particularly limited, and heating wires or the like can be used.

3. Control Unit for the Internal Combustion Engine (ECU)

An idling stop function that automatically stops the internal combustion engine 5 is provided in the internal combustion engine 5 equipped with the reductant supply system 20 to which the present invention is applied. The idling stop function is a function that automatically stops the internal combustion engine 5 when a predetermined idling stop condition is established, for example, when the rotational speed of the internal combustion engine becomes equal to or less than a predetermined value in a state where a key switch of the internal combustion engine is on. The function thus inhibits air pollution caused by exhaust gas and engine sound noise.

FIG. 2 shows an example of the structure of the ECU 70 that is provided with a function to perform idling stop control. The ECU 70 is principally structured by a microcomputer having a known structure. FIG. 2 shows an example of the structure that is represented by functional blocks that correspond to portions relating to the idling stop control.

The ECU 70 of the present embodiment includes, as main elements, a switch state detection portion (denoted by “Swt detection”), a rotational speed detection portion (denoted by “Ne detection”), a vehicle speed detection portion (denoted by “vehicle speed detection”), and an idling stop control portion (denoted by “Idle-Stop control”) that receives detection results from the respective portions and automatically stops the internal combustion engine. These portions are specifically realized by the microcomputer (not shown in the figures) executing a program.

Of these portions, the switch state detection portion detects whether the key switch is either in an on position or an off position, and outputs a signal to the idling stop control portion. The rotational speed detection portion detects the rotational speed of the internal combustion engine, and outputs a signal to the idling stop control portion. Further, the vehicle speed detection portion estimates the vehicle speed based on, for example, the rotational speed of a wheel of the vehicle equipped with the internal combustion engine, and outputs a signal to the idling stop control portion.

Note that detection methods used in the rotational speed detection portion and the vehicle speed detection portion are not particularly limited, and another method other than the above-described methods may be used for detection.

The idling stop control portion determines whether or not a condition for idling stop that automatically stops the internal combustion engine is established, based on the signals transmitted from the above-described respective portions. When the condition is established, the idling stop control portion performs control such that the internal combustion engine is stopped. Here, the idling stop condition can be defined as a case where, for example, the key switch is in an on state, the rotational speed of the internal combustion engine is equal to or less than a predetermined threshold value, and the vehicle speed continues to be equal to or less than a predetermined threshold value for a predetermined period of time.

With the ECU 70 of the present embodiment, when it is detected that the vehicle is stopped even when the key switch is on, a timer count is started. If a predetermined period of time elapses in the same state, it is determined that the idling stop condition is established, and the internal combustion engine is automatically stopped. On the other hand, after the timer count is started, if the vehicle starts to move or the key switch is turned off before elapse of the predetermined period of time, the timer is reset and the idling stop control is cancelled.

Although not shown in the drawings, the ECU 70 of the present embodiment is provided with a restoration control portion that restores the internal combustion engine to an operation state again, when an accelerator lever is depressed or a predetermined switch is turned on after the idling stop condition has been established once and the internal combustion engine has been automatically stopped.

When the idling stop condition is established and the internal combustion engine is automatically stopped, the ECU 70 outputs to the DCU 60 information indicating that the internal combustion engine has been stopped by the idling stop function.

However, the idling stop condition can be determined by adding various factors other than those described above, and is not limited to the above described condition. For example, whether a transmission gear is in a neutral position, or whether a clutch is depressed (in the case of a manual transmission vehicle) may be added as conditions, and whether to automatically stop the internal combustion engine may be determined based on this.

4. Control Unit (DCU) for the Reductant Supply System

FIG. 3 shows the structure of the DCU 60 for controlling the reductant supply system of the present embodiment. Similar to the ECU 70, the DCU 60 is principally structured by a microcomputer having a known structure. FIG. 3 shows an example of the structure that is represented by functional blocks that correspond to portions relating to operation control of the reductant injection valve 31, the pump 41, the reverting valve 71 and the heaters 92 to 97 that are shown in FIG. 1.

The DCU 60 according to the present embodiment includes, as main elements, an idling stop determination portion (denoted by “Idle-Stop determination”), a heating means operation determination portion (denoted by “Heater operation determination”), an energy detection portion (denoted by “Heater power detection”), an outside air temperature detection portion (denoted by “Temp detection”), a heating means control portion (denoted by “Heater control”), a reductant injection control portion (denoted by “Uds control”), and a reverting valve control portion (denoted by “Rtv control”). The respective portions are specifically realized by the microcomputer (not shown in the figures) executing a program.

The idling stop determination portion determines, based on a signal transmitted from the ECU 70, whether or not the internal combustion engine has been stopped by the idling stop control. When it is determined that the internal combustion engine has been automatically stopped, the idling stop determination portion outputs a signal to the heating means control portion, the reductant injection control portion and the reverting valve control portion, which will be described later.

The heating means operation determination portion determines whether or not at least one of the heaters provided in the reductant supply route is in operation. Further, the energy detection portion detects the magnitude of energy supplied from a source of power for operating the heaters provided in the reductant supply route. The source of power is, for example, a battery, and the energy detection portion detects the supply voltage of the battery. Further, the outside air temperature detection portion detects an outside air temperature, based on, for example, output information from a temperature sensor that is installed in a vehicle to detect an outside air temperature.

The determination results and detection results of these portions are respectively transmitted to the heating means control portion.

The heating means control portion stops the operation of the heating means when a predetermined condition is established, based on respective signals transmitted from the idling stop determination portion, the heating means operation determination portion, the energy detection portion and the outside air temperature detection portion. More specifically, the control is basically performed such that: when a signal indicating that the internal combustion engine is automatically stopped is transmitted from the idling stop determination portion, whether or not the heater is in operation is determined based on the signal transmitted from the heating means operation determination portion; and when the heater is in operation, the operation of the heater is stopped.

The DCU 60 of the present embodiment further includes a timer counter (denoted by “Timer 1” in FIG. 3) in the heating means control portion. A time period until the heater is stopped is changed based on information about the supply voltage of the battery transmitted from the energy detection portion, and information about the outside air temperature transmitted from the outside air temperature detection portion. More specifically, the time period until the heater is stopped is defined in advance, in a map, in accordance with the supply voltage of the battery and the outside air temperature, and the map is stored. When the supply voltage of the battery is large, or when the outside air temperature is low, extension of the time period until the heater is stopped is permitted. On the other hand, when the supply voltage is small, or when the outside air temperature is high, the heater is stopped immediately.

For example, under a temperature condition in which the liquid reductant is likely to freeze, the time period until the heater is stopped is varied in accordance with the supply voltage of the battery. When the supply voltage is high, the time period is set to be relatively long, and when the supply voltage is low, the time period is set to be relatively short. This makes it possible to inhibit freezing of the liquid reductant in the reductant supply route when the internal combustion engine is automatically stopped, without significantly reducing the supply voltage of the battery.

On the other hand, under a temperature condition in which the liquid reductant is unlikely to freeze, there is no need to operate the heater. Accordingly, the heater is stopped immediately. This makes it possible to reduce wasteful consumption of the battery, and to remove the possibility of freezing of the liquid reductant.

However, it is not essential that the time period until the heater is stopped is varied based on the supply voltage of the battery and the outside air temperature. Both of the above conditions can be omitted, or the control can be performed taking account of one of the conditions.

In a normal operation state, the reductant injection control portion controls an injection amount of the reductant, based on, for example, information about the reductant in the storage tank, information about an exhaust gas temperature, a reduction catalyst temperature and a NO_(x) concentration on the downstream side of the reduction catalyst, and information about the operation state of the internal combustion engine. On the other hand, when a signal indicating that the internal combustion engine has been automatically stopped is transmitted from the idling stop determination portion, there is no exhaust gas flow. Therefore, the reductant injection valve 31 is closed and the drive of the pump 41 is stopped.

Further, when the signal indicating that the internal combustion engine has been automatically stopped is transmitted from the idling stop determination portion, the reverting valve control portion opens the reverting valve in order to collect the liquid reductant in the reductant supply route into the storage tank.

The DCU 60 of the present embodiment is structured such that a timer counter (denoted by “Timer 2” in FIG. 3) is provided in the reverting valve control portion, and the reverting valve is opened when a predetermined time elapses after the internal combustion engine has been automatically stopped. With this structure, when the internal combustion engine is returned to the operation mode again shortly after it has been automatically stopped by the idling stop control, the liquid reductant is still held in the reductant supply route. Thus, injection control of the liquid reductant is started without delay.

5. Reductant Injection Control

Next, reductant injection control performed by the reductant supply system 20 provided in the exhaust gas purification device 10 shown in FIG. 1 will be described. When the internal combustion engine is in operation, the liquid reductant in the storage tank 50 is pumped by the pump 41 and is pressure-fed to the reductant injection valve 31. At this time, the detection value detected by the pressure sensor 43 that is provided in the first supply passage 58 on the downstream side of the pump 41 is fed back, and is controlled to be a predetermined pressure value. For example, when the detection value is less than the predetermined value, the output of the pump 41 is increased. On the other hand, when the pressure value exceeds the predetermined value, the output of the pump 41 is reduced. At the same time, the liquid reductant is caused to flow back to the storage tank 50 via the pressure control valve 49 and the pressure is reduced. Thus, the pressure of the reductant that is pressure-fed to the reductant injection valve 31 side is maintained at a substantially fixed value.

The reductant that is pressure-fed from the pump module 40 to the reductant injection valve 31 is maintained at a substantially fixed pressure value, and is injected into the exhaust passage when the reductant injection valve 31 is opened. The DCU 60 determines an injection supply amount of the reductant to be injected, based on information such as the operation state and exhaust gas temperature of the internal combustion engine, the temperature of the reduction catalyst 13, and the amount of NO_(x) that has passed through the reduction catalyst 13 without being reduced, the amount of NO_(x) being measured on the downstream side of the reduction catalyst 13. The DCU 60 generates a control signal in accordance with the determined injection supply amount, and outputs it to the reductant injection valve 31. The reductant injection valve 31 is duty controlled by this control signal, and an appropriate amount of reductant is injected and supplied into the exhaust passage. The reductant that is injected into the exhaust passage flows into the reduction catalyst 13, and is used in reductive reaction of NO_(x) contained in exhaust gas.

6. Control of the Internal Combustion Engine in an Automatically Stopped State

Next, an example of the routine of a control method for the reductant supply system 20 will be described with reference to the control flow shown in FIG. 4 to FIG. 6. The control method is performed when the idling stop condition is established and the engine is automatically stopped, in the control unit (DCU) 60 for the reductant supply system of the present embodiment shown in FIG. 3.

First, as shown in FIG. 4, at step S11 after the start, it is determined whether or not the internal combustion engine is automatically stopped by the idling stop control, i.e., it is determined whether or not the internal combustion engine is in an idling stop mode. The DCU 60 of the present embodiment receives a signal from the ECU 70 when the idling stop condition is established and the internal combustion engine is automatically stopped. Therefore, at step S11, the determination is made based on this signal.

FIG. 6 shows an example of the flow of automatic stop control of the internal combustion engine. The automatic stop control is performed by the ECU 70 based on establishment of the idling stop condition.

In this example, first, it is determined at step S1 whether or not the key switch of the internal combustion engine is on. When the key switch is on, the process proceeds to step S2.

At step S2, a rotational speed Ne of the internal combustion engine is detected, and it is determined whether or not the rotational speed Ne is equal to or less than a predetermined reference value Ne0. When the rotational speed Ne is equal to or less than the reference value Ne0, the process proceeds to step S3. The reference value Ne0 is set to a value that can be used to determine the idling state.

Next, at step S3, the vehicle speed is detected, and it is determined whether or not the vehicle speed is equal to or less than a predetermined reference value S0. When the vehicle speed is equal to or less than the reference value S0, the process proceeds to step S4. Generally, the reference value S0 is set to 0 Km/hr so that it can be used to determine that the vehicle is stopped.

If one of the conditions from step S1 to step S3 is not satisfied, the idling stop control is terminated. On the other hand, if all the conditions from step S1 to step S3 are satisfied, the process proceeds to step S4, and a timer is actuated.

Next, at step S5 and step S6, it is determined whether the key switch is turned on during a time period from the actuation of the timer until the elapse of a reference time T0, and whether the rotational speed Ne of the internal combustion engine is equal to or less than the reference value Ne0. If the key switch is turned off before the elapse of the reference time T0, or if the rotational speed Ne of the internal combustion engine exceeds the reference value Ne0, the idling stop control is terminated.

On the other hand, if the reference time T0 has elapsed while the key switch remains on and the rotational speed Ne of the internal combustion engine remains equal to or less than the reference value, the process proceeds to step S7 and the internal combustion engine is stopped. Thus, the idling stop control is terminated.

Although not shown in the figures, a signal indicating that the internal combustion engine has been stopped by the idling stop control is output to the DCU.

Note that, if the DCU is designed to directly determine whether or not the idling stop condition is established, step S11 of the control flow in FIG. 4 can be replaced with step S1 to step S7 of the control flow in FIG. 6.

Returning now to FIG. 4, if it is determined at step S11 that the internal combustion engine has been automatically stopped, the process proceeds to step S12, and it is determined whether or not at least one of the heaters 92 to 97 provided in the reductant supply route is in operation. When all the heaters 92 to 97 are not in operation, the process proceeds to step S20 in FIG. 5. On the other hand, when at least one of the heaters is in operation, the process proceeds to step S13.

Next, at step S13, the value of the supply voltage of the battery that supplies voltage to the heater, and the outside air temperature are detected. After that, at step S14, a timer 1 value Ta0, which is a time period until the operation of the heater is stopped, is calculated based on the supply voltage of the battery and the outside air temperature.

For example, the time period until the heater is stopped is defined in advance, in a map, in accordance with the supply voltage of the battery and the outside air temperature, and the map is stored, so that the time period can be read. Under a temperature condition in which the liquid reductant is likely to freeze, when the supply voltage is high, the time period is set to be relatively long, and when the supply voltage is low, the time period is set to be relatively short. On the other hand, under a temperature condition in which the liquid reductant is unlikely to freeze, there is no need to operate the heater. Accordingly, the heater is stopped immediately.

If the timer 1 value Ta0 is determined at step S14, the timer 1 is actuated and a count is started at step S15. Next, at step S16 and step S17, it is determined whether or not the rotational speed Ne of the internal combustion engine is equal to or less than the reference value Ne0 during a time period from the actuation of the timer 1 until the elapse of the timer 1 value Ta0. If the rotational speed Ne of the internal combustion engine exceeds the reference value Ne0 before the elapse of the timer 1 value Ta0, the internal combustion engine is back to the operation state again, and the injection control of the liquid reductant is restarted. Therefore, the process proceeds to step S19, and the timer 1 is reset to continue the operation of the heater. Then, the process ends.

On the other hand, if the timer 1 value Ta0 has elapsed while the rotational speed Ne of the internal combustion engine remains equal to or less than the reference value Ne0, the process proceeds to step S18, and power supply to the heater is shut off to stop the operation of the heater. After that, the process proceeds to step S20. There is no exhaust gas flow in a state where the internal combustion engine is stopped by the idling stop control, and the injection control of the liquid reductant is not performed. Therefore, if the operation of the heater is stopped when a predetermined time elapses in an idling stop state, it is possible to prevent wasteful consumption of the battery due to continuous operation of the heater.

At step S16, whether or not the internal combustion engine has returned to the operation state again is determined based on the rotational speed Ne of the internal combustion engine. However, it may be determined based on another condition, for example, whether or not the accelerator is depressed.

After the operation of the heater is stopped, from step S20 onwards, control to collect the residual liquid reductant of the reductant supply route is performed.

First, the timer 2 is actuated at step S20. Then, at step S21 and step S22, it is determined whether or not the rotational speed Ne of the internal combustion engine is equal to or less than the reference value Ne0 during a time period from the actuation of the timer 2 until the elapse of a timer 2 value Tb0. If the rotational speed Ne of the internal combustion engine exceeds the reference value Ne0 before the elapse of the timer 2 value Tb0, the internal combustion engine is back to the operation state again, and the injection control of the liquid reductant is restarted. Therefore, the process proceeds to step S24, and the timer 2 is reset without collecting the liquid reductant of the reductant supply route. Then, the process ends.

On the other hand, if the timer 2 value Tb0 has elapsed while the rotational speed Ne of the internal combustion engine remains equal to or less than the reference value Ne0, the process proceeds to step S23, and the drive of the pump 41 is stopped. Meanwhile, the reverting valve 71 is driven to collect the residual liquid reductant in the reductant supply route into the storage tank 50. As a result, when the internal combustion engine is stopped by the idling stop control, the operation of the heater is stopped and the liquid reductant is collected. Thus, wasteful consumption of the battery is inhibited. In addition, freezing or crystallization of the liquid reductant in the reductant supply route can be prevented.

Note that, although the operation of the heater is stopped at the previous step S18, a time period from when the operation of the heater stops to the collection of the liquid reductant is short. Therefore, it is ensured that freezing of the liquid reductant does not occur during this time period.

7. Another Structure Example

The control flow that has been described above is only an exemplary embodiment, and can be performed by omitting some of the steps or by switching their order.

For example, when the control to collect the liquid reductant is performed, the above-described step S20 to step S22 may be omitted, in order to ensure that the liquid reductant is always collected when the operation of the heater is stopped.

Further, if the control to collect the reductant at step S20 to step S24, and the control to stop the heater at step S12 to step S19 are performed by switching the order, the operation of the heater is stopped after the liquid reductant has been collected. Therefore, freezing of the liquid reductant is inhibited reliably.

Moreover, the present embodiment is described using, as an example, the reductant supply system of a type that directly injects, into the exhaust pipe from the reductant injection valve, the liquid reductant that is pressure-fed by the pump. However, the present invention can be applied not only to a reductant supply system of this type, but also to a reductant supply system of an air assisted type, which supplies reductant into a mixing chamber via a valve for adjusting the flow rate of the reductant that is pressure-fed by a pump, and supplies the reductant into an exhaust pipe while atomizing it using high-pressure air. 

1-9. (canceled)
 10. A control unit for a reductant supply system, which performs control of a reductant supply system which is used in an exhaust gas purification device that injects and supplies a liquid reductant to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst, the reductant supply system having a storage tank that stores the liquid reductant, a pump that pressure-feeds the liquid reductant stored in the storage tank, a reductant injection valve that controls a supply amount of the liquid reductant that is pressure-fed by the pump, and a reductant supply passage through which the liquid reductant is caused to flow, the control unit comprising: an idling stop determination portion that determines whether the internal combustion engine is stopped by idling stop control that automatically stops the internal combustion engine; a heating means operation determination portion that determines whether heating means provided in a reductant supply route that supplies the liquid reductant to the reductant injection valve is in operation; and a heating means control portion that stops operation of the heating means in a state where the internal combustion engine is automatically stopped and the heating means is in operation.
 11. The control unit for a reductant supply system according to claim 10, wherein the heating means control portion stops the operation of the heating means when a predetermined period of time elapses after it is determined that the internal combustion engine has been automatically stopped.
 12. The control unit for a reductant supply system according to claim 10, further comprising an outside air temperature detection portion that detects outside air temperature information, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.
 13. The control unit for a reductant supply system according to claim 11, further comprising an outside air temperature detection portion that detects outside air temperature information, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.
 14. The control unit for a reductant supply system according to claim 10, further comprising an outside air temperature detection portion that detects outside air temperature information, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.
 15. The control unit for a reductant supply system according to claim 11, further comprising an outside air temperature detection portion that detects outside air temperature information, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.
 16. The control unit for a reductant supply system according to claim 12, further comprising an outside air temperature detection portion that detects outside air temperature information, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.
 17. The control unit for a reductant supply system according to claim 13, further comprising an outside air temperature detection portion that detects outside air temperature information, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the outside air temperature.
 18. The control unit for a reductant supply system according to claim 10, further comprising an energy detection portion that detects a magnitude of energy supplied from a source of power of the heating means, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the magnitude of the energy.
 19. The control unit for a reductant supply system according to claim 11, further comprising an energy detection portion that detects a magnitude of energy supplied from a source of power of the heating means, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the magnitude of the energy.
 20. The control unit for a reductant supply system according to claim 12, further comprising an energy detection portion that detects a magnitude of energy supplied from a source of power of the heating means, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the magnitude of the energy.
 21. The control unit for a reductant supply system according to claim 14, further comprising an energy detection portion that detects a magnitude of energy supplied from a source of power of the heating means, wherein the heating means control portion changes a time period from when it is determined that the internal combustion engine is automatically stopped until when the heating means is stopped, in accordance with the magnitude of the energy.
 22. The control unit for a reductant supply system according to claim 10, further comprising a reductant return control portion that causes the liquid reductant of the reductant supply route to be collected into the storage tank when the internal combustion engine is automatically stopped.
 23. The control unit for a reductant supply system according to claim 11, further comprising a reductant return control portion that causes the liquid reductant of the reductant supply route to be collected into the storage tank when the internal combustion engine is automatically stopped.
 24. The control unit for a reductant supply system according to claim 21, further comprising a reductant return control portion that causes the liquid reductant of the reductant supply route to be collected into the storage tank when the internal combustion engine is automatically stopped.
 25. The control unit for a reductant supply system according to claim 22, wherein the reductant return control portion collects the liquid reductant when a predetermined period of time elapses after it is determined that the internal combustion engine has been automatically stopped.
 26. The control unit for a reductant supply system according to claim 5, wherein the reductant return control portion collects the liquid reductant when a predetermined period of time elapses after it is determined that the internal combustion engine has been automatically stopped.
 27. The control unit for a reductant supply system according to claim 10, wherein the idling stop determination portion determines that the internal combustion engine has been automatically stopped when at least a key switch of the internal combustion engine is on and when a rotational speed of the internal combustion engine continues to be equal to or less than a predetermined value for a predetermined period of time.
 28. The control unit for a reductant supply system according to claim 10, wherein the idling stop determination portion determines whether the internal combustion engine has been automatically stopped, based on a signal from an engine control unit that performs operation control of the internal combustion engine.
 29. A control method for a reductant supply system which is used in an exhaust gas purification device that injects and supplies a liquid reductant to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst, the reductant supply system having a storage tank that stores the liquid reductant, a pump that pressure-feeds the liquid reductant stored in the storage tank, a reductant injection valve that controls a supply amount of the liquid reductant that is pressure-fed by the pump, and a reductant supply passage through which the liquid reductant flows, the control method comprising the steps of: determining whether heating means provided in a reductant supply route is in operation in a state where the internal combustion engine is stopped by idling stop control that automatically stops the internal combustion engine; and stopping operation of the heating means when the heating means is in operation. 